Method of making inherently stable jet fuels



METHOD oF MAKING INHERENTLY STABLE JET FUELS Filed oct. 27. 1961 J. A.FAVRE Nov. 9, 1965 2 Sheets-Sheet 1 METHOD oF MAKING INHERENTLY STABLEJET FUELS Filed 0013. 27. 1961 J. A. FAVRE Nov. 9, 1965 2 Sheets-Sheet 2TO CONDUIT 36 FEEDj l7 74 TO MOTOR F U E L 5 3 E Tw WZ G VN N8 Lw .m5 OTSC NK A ...LEN OR BA TT T X O E T 5 l 6 7 J 5 G F FEEDJ INVENTOR. J. A.FAVRE United States Patent 3,216,929 METHOD F MAKING INHERENTLY STABLEJET FUELS John A. Favre, Bartlesville, Okla., assigner to PhillipsPetroleum Company, a corporation of Delaware Filed Oct. 27, 1961, Ser.No. 148,155 Claims. (Cl. 208-312) This invention relates to ahydrocarbon fuel and to a process and apparatus for preparing the same.In one of its aspects, the invention relates to a process and apparatusfor removing high-boiling aromatic compounds from a hydrocarbon fuel,and to the fuel thus produced. In another aspect, the invention relatesto process and apparatus for separating a hydrocarbon fuel into variousboiling-range cuts, removing detrimental compounds from certain of thesecuts, and combining the cuts to produce a hydrocarbon fuel. In stillanother aspect, the invention relates to method and apparatus forremoving detrimental compounds such as indene and indane and/orcompounds containing hydroxyl radicals and/or sulfur from a hydrocarbonfuel, and to the fuel thus produced.

The modern jet aircraft are fueled by relatively inexpensive middlefractions, that is, from straight run or cracked and reformed stock fromwhich the gasoline has been recovered; further distillation yields afraction which has been suitable for jet fuel. It is customary to limitthe end point by ASTM distillation to 600 F., to remove sulfur compoundsand to reduce aromatics to 25 percent by volume. This practice ofleniency in specification has been helpful to the refiners in that theyhave been able to supply the large volume of jet fuels demand with onlyslight infringement and consequent unbalance of motor fuel blendingstocks.

Recent indications based on field observations are that it will benecessary to tighten Ithe `specifications on jet fuels. The reason forfailure is not on the combustion characteristics of the fuel, but ratherbecause icing prior to the filtering step caused filter plugging andresulted in flame-out. Preheaters installed ahead of the filterscorrected the icing tendency, but caused heavy deposits to be laid downin the preheater and filter plugging by carbonaceous deposits.

It is an object of this invention to prepare a jet fuel having stabilityat the preheater temperature range. It

is another object of this invention to provide a jet fuel which does notlay down deposits in the preheater or plug the fuel filter in the jetengine system when utilized. It is another object of fthe invention toprovide a method and apparatus whereby stabilized jet fuels can beprepared Without undue unbalance of refinery inventories.

Other aspects, objects, and the several advantages of the invention willbecome apparent to one skilled in the art upon a study of thisdisclosure, drawing, and the appended claims.

In accordance with this invention the above objects are attained byseparating a mixture boiling in the range about to 600 F. (by ASTMdistillation) into three fractions; initial to 320 F., S20-400 F. and400 F.-i;

'removing aromatics from the 400 F.l fraction and from the initial to320 F. fraction; and blending the nonaromatic constituents from allfractions with aromatics from the middle fraction with or without priorseparation so that the resulting jet fuel contains from 1 to 25 percentby volume of the middle boiling aromatics. In one embodiment, themixture treated comprises a naphtha re- 3,216,929 Patented Nov. 9, 1965e. CC

sulting from reforming of a catalytically cracked cycle oil. In anotherembodiment, a high-boiling portion of aromatics separated from thelow-boiling (i.e., initial to 320 F.) fraction of the feed mixture, aswell as aromatics from the middle (i.e., 320-400 F.) fraction, areblended into the jet fuel product. In another embodiment, a cut fromabout 350 F. to about 360 F. containing the detrimental compounds indeneand indane is removed from the fuel. This latter removal can beaccomplished either by a further fractionation of the above-referred-tomiddle or 320-400 F. cut with removal of the indaneindene containing cutas a sidedraw therefrom, or by separating the feed mixture into threefractions; initial to 350 F., S50-400 F., and 400 R+; topping the middleor 350-400 F. cut to remove indene and indane; and then treating thethree remaining cuts as stated above.

It has been suggested in the prior art that condensed ring aromaticcompounds are detrimental to hydrocarbon fuels, and to jet fuels inparticular, while alkylated single ring aromatics are not detrimental.This suggestion in the prior art is directed toward the problem of iceformation in the fuel, which causes plugging of the fuel filter asstated previously. Icing has, as stated, been prevented by preheatingthe fuel prior to its filtration. I have noW discovered that theresulting problem of filter plugging caused by carbonaceous depositsresulting from preheating the fuel can be eliminated by use of a fuelfrom which essentially all aromatic compounds boiling above about 400 F.have been removed. I have further discovered that the presence of notonly higher-boiling aromatic compounds, but also compounds of the sameboiling range containing hydroxyl radicals and/or sulfur and thebicyclics indene and indane, are detrimental to the thermal stability ofa jet fuel and can be substantially completely removed by the process ofmy invention.

FIGURE l is a flow diagram of a presently preferred embodiment of theinvention.

FIGURE '2 illustrates a method for removing a narrow boiling rangeintermediate cut.

FIGURE 3 illustrates alternative apparatus for removing a narrow boilingrange middle cut.

In order to provide a more complete understanding of my invention,reference is now made to the accompanying drawing, which is a flowdiagram of a presently-preferred embodiment of my invention. In FIGUREl, a suitable hydrocarbon feed is passed by way of conduit 1 to afractionation column 2. The feed is fractionated in the column toproduce an overhead stream 3 preferably boiling in the range 50-320 F.,an intermediate stream 4 preferably boiling in the range 320-400 F., anda kettle product 5 preferably boiling in the range 400-600 F. Theoverhead stream is passed by way of conduit 3 to a solvent extractionzone 6, wherein it is contacted with an aromatic-preferential solventintroduced into the zone by way of conduit 7. A raffinate stream isremoved from zone 6 (IAF 10-24-61) and passed by Way of conduit 8 to astripping zone 9, wherein residual solvent is removed. An aromatic-freerafiinate is recovered overhead by Way of conduit 12; recovered solventis returned by way of conduits 13 and 7 to the extraction zone 6.Solvent rich in aromatics is recovered from extraction zone 6 and passedby Way of conduit 14 to a heated ash zone 15. Aromatics flashed from thesolvent are taken overhead by way of conduit 16 to a fractionator 17,and solvent containing heavier aromatics is passed by way of conduit 18to a secondary ash zone 19. Aromatics removed in this zone can be passedby way of conduit 21 and its associated valve to a refrigeratedseparator 22, or can alternately be passed by Way of conduit 23 and itsassociated valve through conduit 16 to fractionator 17. Solventcontaining still heavier aromatics is passed by way of conduit 24 to avacuum flash zone 25; aromatics recovered here are passed by way ofconduits 26 and 21 to separator 22. Recovered solvent is returned by wayof conduits 27 and 7 to extraction zone 6. It is to be understood thatash zones 15, 19, and 25 are operated at progressively lower pressuresas known in the art. Solvent passed by way of conduit 21 to separator 22is cooled to cause separation of a solvent phase returned by way ofconduit 34 to secondary flash zone 19 and an extract phase removed byway of conduit 32. This latter phase can be passed by way of conduit 33to extraction zone 6, can be added via conduit 32 to fuel blending tank58, or can be removed as an aromatic product by Way of conduit 30.

The intermediate stream from column 2 can be passed by way of conduit 4and its associated valve to a second solvent extraction zone 35, whichpreferably uses the same type solvent as does zone 6. Alternately, thisintermediate cut can be passed directly to blending tank 58 by way ofconduit 36 and its associated valve. A portion of. the cut can bewithdrawn by way of conduit 37 for use in motor fuel if desired. Theintermediate fraction passed to extraction zone 35 is contacted thereinwith solvent introduced by way of conduit 38; this solvent can, ifdesired, be obtained from the previously-described solvent extractionsystem by way of conduit 40. A solvent extract rich in` aromatics isremoved from zone 35 and passed by way of conduit 39 to a stripper 41:wherein aromatics are stripped from the solvent and passed by way ofconduit 42 to blending tank 58. Solvent is returned to extraction zone35 by Way of conduit 38, and excess solvent can be withdrawn from thesystem by way of conduit 43. A raflinate free from aromatics iswithdrawn from extraction zone and passed by way of conduit 44 to astripper 45, wherein entrained solvent is removed. The resultingaromatic-free stream is passed by way of conduit 46 to blending tank 58.Recovered solvent is passed by way of conduit 47 to conduit 38.

The high-boiling stream from fractionator 2 is passed by way of conduit5 to one of a pair of cyclically-operating adsorbers 48 whereinaromatics and other detrimental components of the stream are retained onan adsorbent such as silica gel or a molecular sieve. The resultingaromatic-free stream is passed by way of conduit 49 to blending tank 58.Adsorbent in vessels 48 can be regenerated by flushing rst with a streamof methanol and then hot butane, both introduced by way of conduits 56and 51. Desorbent is removed by way of conduit 52 to a desorbentrecovery zone 53 wherein methanol and butane are recovered for re-use byway of conduit 54, and a heavy aromatics stream is removed by way ofconduit 55.

The light aromatics-free raffinate stream in conduit 12 can be partiallywithdrawn by way of conduit 11 for use as a motor fuel blending stock,but is preferably passed to blending tank 58. If it is desired to adjustthe volatility of the fuel product, this light stream in conduit 12 canalternately be by-passed by way of conduit 65 and its associated valveto a topping column 64, wherein light ends are removed for motor fuelblending by way of conduit 63. The remainder of the cut is passed by wayof conduits 62 and 12 to blending tank 58. In addition to streams 12,32, 36, 42, 46, and 49, previously described as being added to blendingtank 58, there can be added other components such as additives by way ofconduit 59 (eg. antioxidants) and butane by way of conduit 61 for nalvolatility adjustment. The desired jet fuel is withdrawn by way ofconduit 66.

It will be evident to one skilled in the art that various necessary ordesirable pieces of equipment, such as heat exchangers, boilers, valves,control means, pumps, storage vessels, mixers, and the like, have beenomitted from the drawing for the sake of clarity.

Typical conditions useful in operation of the equipment of the figureare as follows.

Extraction zone 6:

Pressure 25400 p.s.i.g. Temperature 230-240 F. Solvent (diethyleneglycol) 240-250 F. Extraction zone 35:

Pressure 25-100 p.s.i.g. Temperature Z-300 F. Solvent (diethyleneglycol) 3D0-350 F. Flash zone l5 Z50-300 F., 15-20 p.s.i.g. Flash zone19 300 F., atmospheric pressure..

Feedstocks useful in the practice of my invention will` typicallycontain 25 to 80 volume percent or more of aro-- matics and thus wouldnot meet the jet fuel requirement; of 25.0 percent maximum aromaticcontent. These feedstocks will vary somewhat in composition but willhave a boiling range of about 50 to about 600 F. with both initial andend point variable. A typical reformed catalytically cracked naphthasuitable for use in my invention has the following properties:

Gravity API 43.9 ASTM Distillation, F.:

I. B.P 80 5 109 10 130 20 178 30 230 40 250 50 263 Rec 94.0

Rs. L2

Loss 4.8 Reid Vapor Press, p.s.i 16.7 Naphthenes and parains, vol.percent 25.3 Olens, vol. percent 0.3 Aromatics, vol. percent 74.4

Using the method of this invention, the following products can beobtained from this feedstock based on 1,000 bbls. of reformed naphthacharged.

Stream Product Volume,

N o. bbls.

3 OHP (Initial, 320 F.) 830 4 (36) MP (32o-400 F.) 120 5 BP (40G-H.v 50Total Charge 1000 Init., 320 F. Paralimic Naphtha. 105 Init., 250 F.Paralnic Naphtha. 122 (3g-Cm ParafIin-naphtheues 43 Benzene 92 TolueneC3 Aromatics 326 Naphthene-parallins (S20-400 F.) 47 Aromatics (S20-400F.) 73 Cgi-Cw Aromatics 6l 400+ Paraln-naphthene 44 Diand poly-cyclicaromatics 6 .IP-6 fuel @5G-485 F.) 178 Blend Composition: Bbls. Stream62 43 Stream 46 47 Stream 49 44 Stream 42 44 Total Stream 66 178 PercentAromatics 24. 7 Specific Gravity 0. 788

9 a, F Final End Point, F-- Residue, percent.. Loss, percent- FreezingPt., F Corrosion (212 F., 3 hr Sulfur, Wt. percent Aromatics, Vol.percent Bromine Number (cg./g.) Viscosity at 40 F. centistokes Residue(400 F. Air jet), mg./100 ml. Net Heat of Combustion, B.t.u./lb 16 hr.Accelerated Gum, rug/100 ml.. Thermal Stability The following specificexamples will serve to illustrate the advantages of my invention.

EXAMPLE I In order to show the effect of the process on the perormanceof a jet fuel made thereby, the following tests were performed. The basefuel was a 400+ fraction from a JP-6 type jet fuel. This fraction wasselected because it is believed to be the portion causing deposits inpreheater and lilter plugging during operation. The material wasnon-aromatic. 'Ihermal stability tests were run using a CFR Fuel Cokerat a fuel-out temperature of 450 F.

The base oil resulted in a pressure drop across the lter of only 0.13mercury pressure after 300 minutes operation yand the preheater tubeWalls had a C-FR color rating of 1 (slight haze, no color).

The base oil with 1.0 weight percent alpha-methylnaphthalene requiredonly 223 minutes operation to result in a 25 mercury pressure dropacross the filter, and to form a bronze lacquer on the preheater tubesresulting in a CFR color rating of 4 whereas a 2 rating is consideredbad and lb (light tan) coloration is permitted.

To test the purity of the alpha-methylnaphthalene, it was redistilledand a second run was made with the base oil containing 1.0 weightpercent of the redistilled alphamethylnaphthalene. A pressure drop of 25mercury pressure developed across the lter in 215 minutes and again theCFR color rating was 4.

In a test of the 'base oil with 1.0 weight percent triethyl benzene,after 300 minutes operation only 0.02" mercury pressure drop haddeveloped across the iilter and a CFR color rating of 0 was givenbecause no visible color or deposit appeared on the preheater tubing.

Thus by removing the fused ring aromatics and adding alkyl aromatics ahighly thermostable jet fuel is produced whose stability is superior tonon-aromatic or highly volatile jet fuels which have been suggested forthis service.

EXAMPLE II Table l Filter Pressure Heater Deposit Test Drop, RatingInches Mercury Base oil #l 0.00 0 (no visible deposits). Base oil #lplus:

0.25 vol. percent redistilled AMN-- 0. 37 "3 (light tan deposits). 0.45vol. percent redistilled AMN-- 0. 35 5 (tan deposits and heavier). 0.45vol. percent percent pur- 0.78 1 (slight haze,

ity AMN. no color).

When heterocyclics, i.e. ring sulfur compounds, are present in the fuel,the total of heterocyclics and bicyclic aromatics must be below 0.45volume percent and preferably should be absent in JP-6 type fuels.Distillation and solvent extraction are ineffective in making theseparation between bicyclic aromatics and heterocyclics boiling in thesame temperature range, that is, above about 400 F. It has been foundthat adsorption is effective to remove these high-boiling heterocyclics.A further important feature of my invention resides in the discoverythat there exists near the cut point (ie. about 392 F. to about 400 F.)between the intermediate and the high-boiling fractions a wide gapbetween the boiling point of the desired mononuclear aromatics and thedetrimental bicyclic aromatics.

The preceding examples and FIGURE l are particularly useful when thereis no indene or indane present in the feedstock. Presence of either orboth of these compounds makes desirable a modification of the method setforth in FIGURE l. Referring now to FIGURE 2, it is seen that the middleor 320-400 F. cut in conduit 4 is passed to a fractionator 67 whereinthe indene and/ or indane is removed as a sidedraw comprising materialboiling from about 350 F. to about 360 F. by Way of conduit 68. Overheadfrom this column is passed by way of conduits 69, 70, and 36 to blendingtank 58. Alternatively, this cut can be passed by way of conduit 71 toconduit 72 wherein it is admixed with kettle product therein fortreatment in solvent extraction zone 35 to remove aromatics as describedin conjunction with FIGURE l.

Another method for removal of indene and/ or indane is shown in FIGURE3. In accordance with this method, fractionation column 2 is operated toproduce the follow ing streams: overhead in conduit 3', initial, 350 F.;sidedraw in conduit 4', S50-400 F.; and kettle product in conduit 5, 400F.-|-. The material in conduits 3', and 5 is treated as in FIGURE 1. Thecenter cut in conduit 4 is passed to a topping fractionator 73, whereinthe overhead containing indene and/or indane is removed by way ofconduit 74 for use as motor fuel; this cut boils preferably from about350 F. to about 360 F. The remainder of this center cut is preferablytaken as kettle product by way of conduit 75 to fuel blending tank 58,but can be treated to remove aromatics by passing via conduit 76 tosolvent extraction zone 35.

In order to show the detrimental effects of indene and indane, thefollowing tests were made.

EXAMPLE III The same base oil used in Example 1I was used to show theeffect of small additions of indene and indane on the thermal stabilityof the oil in a CFR Fuel Coker test. The same conditions were used as inExample II.

Table II is a compilation of the data.

When indene or indane are present in the fuel to the extent of 1 percentor more, the fuel lays down deposits in the preheater which exceed thepermitted deposits in accordance with the CFR Fuel Coker test.

As will be obvious from this disclosure and these examples, there areprovided process and apparatus for producing a hydrocarbon fuel whichcomprises fractionating an `aromatics-containing hydrocarbon feedboiling in the range from about 50 F. to about 600 F. to form threefractions, a first low boiling fraction, a second intermediate boilingfraction, and a third high boiling fraction which contains detrimentalaromatics usually boiling above about 400 F.; removing aromatics fromthe rst and the third fractions; and blending the non-aromatic portionsof the first and the third fractions with the second fraction to producea hydrocarbon fuel containing from about 1 to about 25 volume percentaromatics.

Reasonable variation and modification are possible within the scope ofthis disclosure, the appended claims, and the drawing of the invention,the essence of which is that there is provided a hydrocarbon fuel freeof aromatic compounds boiling above about 400 F. and indene and indaneand containing from about 1 to about 25 volume percent of intermediatearomatics boiling in the range of about 300 F. to about 400 F., and amethod and apparatus for preparing the same.

I claim:

1. A process for producing a hydrocarbon fuel from a reformedcatalytically-cracked highly aromatic naphtha feed having a boilingrange of about 50 F. to about 600 F. which comprises fractionating saidfeed into three fractions, a first fraction having a boiling range ofabout 50 F. to about 320 F., a second fraction having a boiling range ofabout 320 F. to about 400 F., and a third fraction having a boilingrange of about 400 F. to about 600 F.; treating said first fraction bysolvent extraction to remove aromatics therefrom; treating said thirdfraction by adsorption to remove aromatics therefrom; and blending thethus-treated first and third fractions with said second fraction toproduce a fuel containing from about 1 to about 25 volume percent ofaromatics boiling in the range of about 300 F. to about 400 F.

2. The process of claim 1 wherein there is further added to saidresulting blend a high-boiling portion of the aromatics removed fromsaid first fraction.

3. The process of claim 1 wherein said second fraction is treated toremove aromatics therefrom prior to said blending step, and whereinaromatics thus removed are admixed in said blending step to produce thedesired hydrocarbon fuel.

I4. The process of claim 1 wherein the aromatics in said fuel have aboiling range from about 300 F. to about 392 F.

5. The process of claim 4 wherein said feed comprises a reformedcatalytically-cracked naphtha.

6. The process of claim 1 wherein there is removed from said secondfraction prior to said blending a portion boiling from about 350 F. toabout 360 F.

7. The process of claim 1 wherein said first fraction boils from about50F. to about 350 F. and said second fraction boils from about 350 F. toabout 400 F. and wherein said second fraction is topped to about 360 F.prior to said blending.

8. A process for producing a hydrocarbon fuel containing not more than25 volume percent aromatics comprising the steps of:

(a) passing a feed comprising a reformed naphtha containing from about25 volume percent to about 80 volume percent aromatics to a separationzone;

(b) separating the feed of step a into a first fraction having a boilingrange of about 50 F. to about 320I F., a second fraction having aboiling range of about 320 F. to about 400 F. and a third fractionhaving a boiling range of about 400 F. to about 600 F.;

(c) treating said first fraction by solvent extraction to removearomatics therefrom whereby to obtain a first product streamsubstantially free of aromatics;

(d) treating said third fraction by adsorption to remove aromaticstherefrom whereby to obtain a second product stream substantially freeof aromatics; and

(e) blending together said rst product stream, said second productstream and said second fraction whereby to obtain a resultinghydrocarbon fuel comprising only components present in the said feed tostep a and whereby the aromatics content is in the range of about 1volume percent to about 25 volume percent.

9. A process according to claim 8 wherein the said second fraction isfurther separated prior to blending to remove components boiling in therange from about 350 F. to about 360 F. therefrom.

10. A process according to claim 8 wherein at least a Vportion of thearomatics removed in step c are also added to the blending of step e.

References Cited by the Examiner UNITED STATES PATENTS 2,345,934 4/44Gregory 196-155 2,388,732 11/45 Finsterbusch 196-155 2,749,225 6/56Barnum et al. 208--15 2,892,769 6/59 Frazier et al 208-15 2,910,42610/59 Gluesenkamp et al 208-66 3,015,549 1/62 Ciapetta et al 208-15FOREIGN PATENTS 870,474 6/ 61 Great Britain.

ALPHONSO D. SULLIVAN, Primary Examiner.

JOSEPH R. LIBERMAN, Examiner.

1. A PROCESS FOR PRODUCING A HYDROCARBON FUEL FROM A REFORMEDCATALYTICALLY-CRACKED HIGHLY AROMATIC NAPHTHA FEED HAVING A BOILINGRANGE OF ABOUT 50*F. TO ABOUT 600* F. WHICH COMPRISES FRACTIONATING SAIDFEED INTO THREE FRACTIONS, A FIRST FRACTION HAVING A BOILING RANGE OFABOUT 50* F. TO ABOUT 320*F., A SECOND FRACTION HAVING A BOILING RANGEOF ABOUT 320*F. TO ABOUT 400*F., AND A THIRD FRACTION HAVING A BOILINGRANGE OF ABOUT 400*F. TO ABOUT 600*F.; TREATING SAID FIRST FRACTION BYSOLVENT EXTRACTION TO REMOVE AROMATICS THEREFROM; TREATING SAID THIRDFRACTION BY ADSORPTION TO REMOVE AROMATICS THEREFROM; AND BLENDING THETHUS-TREATED FIRST AND THIRD FRACTIONS WITH SAID SECOND FRACTION TOPRODUCE A FUEL CONTAINING FROM ABOUT 1